1. Tissue Engineering Technique
Regeneration of Skull Bone through Tissue Engineering Techniques
Modinat Adaranijo, Michelle Davis
Abstract
The bones of the neurocranium are highly susceptible to defects when impacted by certain levels of trauma, disease, tumor ablation, or congenital dysmorphia. Thus, there is an urgent need for the reconstruction and regeneration of these bones because they serve as a great importance in protecting and housing the brain. Autografts, are considered the “gold standard” in clinical care due to its osteoconductive and osteoinductive nature. However, their use is limited due to donor site morbidity coupled with a time-consuming surgical procedure. Other materials, such as alloplastic implants and allogeneic grafts, have been considered and used clinically in the reconstruction of cranial defects. Nonetheless, there is still the issue of immunological reactions as these materials are foreign and will always remain foreign to the biological system. This review article covers different tissue engineering-based strategies as most promising and attractive alternative approach to autologous bone grafts in regards to the regeneration of critical-sized cranial defects. However, these strategies are complicated be scarring, osteomyelitis, osteonecrosis or damage resulting from previous radiation due to the combined use of growth factors such as cytokines, stem cells, and scaffold biomaterials. Thus, strategies and materials must be refined in the future to achieve more reliable surgical outcome and overcome some challenges in real clinical situations where skull reconstruction is needed.
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Vascularization
Fabrication Technique
Conclusion
In the future, various strategies and biomaterials must be refined to further achieve more reliable outcomes and to address the various challenges posed by real clinical scenarios in which skull reconstruction is appropriate. Also, more studies is needed to completely evaluate co-morbidities as well as other severe medical outcomes that is associated with the use of tissue engineering approaches and methods in which these complication can be prevented.
Introduction
The cranium or skull is a part of the skeletal system that serves as protection for the brain and reinforcement for the face. It is of two part,; the viscerocranium which is connected to the braincase which underlies the structures of the face, forms the nasal fossa, orbitals, and supports the teeth of the upper and lower jaws and the neurocranium which is the upper and posterior portion of the skull which protects the brain, brainstem, middle and inner ear structures [1, 2, 3].
RECONSTRUCTIVE TECHNIQUE
(Cranioplasty)
Autograft e.g. bone from the skull, ribs e.t.c.
Allograft e.g. bone from another donor
Alloplastic Implant e.g. Acrylic implant.
Advantages:
Retains most osteogenic cells.
Doesn’t trigger immunoresponsive.
Disadvantages:
Low amount of bone quality.
Risk of graft resorption
Tendency of graft refusal.
Availability of bone graft.
High cost.
Less than ideal mechanical properties
risk of disease transmission
Abundant implant .
Easy to handle and Shape
Hold minimal risk of bone resorption
Possibility of graft rejection and infection.
Tissue Engineering Technique
Osteoblastic Stem cells e.g. BM-MSCs, ADSCs, USCs e.t.c
Osteoconductive Scaffold e.g. polymers, metals, ceramics, e.t.c
Osteoconductive Growth Factor e.g. PDGF, FGF, VEGF e.t.c
Fig 2. The tissue engineering-based technique generally involves three key elements, which include the incorporation of osteoconductive scaffolding, stem cells, and growth factors as shown in all of which allow osteoprogenitor and endothelial progenitor cell differentiation, bone tissue integration, and bone formation
Fig 1. Varieties of reconstructive materials used in cranioplasty
Vascularization is quite important and crucial for bone growth when using the tissue engineering technique. It can be accomplished in three ways;
Impregnating scaffold with VEGF or other angiogenic promoting substances [4].
Seeding the scaffold with endothelial or vasculogenic cells [5].
Implanting the scaffold into highly vascular tissue [6].
This allow implants to be fabricated in a patient specific manner. It include;
Rapid prototyping: used when constructing the prefabricated PMMA implant [7].
Electron beam melting technology: used for metal 3D printing and involves the use of a variety of electron beams to melt and weld very fine metal powder [8].
Reference
Cranial skeletal repair via tissue engineering remains the most promising alternative to autologous bone grafts. Innovation of biocompatible materials and the basic understanding of molecular biology have enabled tissue engineers to make progressive steps towards the regeneration of cranial bone. Also, the combination of different sources of biomaterials, the fabrication of an osteoinductive scaffold, and the incorporation of a variety of stem cells, growth factors, and vasculogenic cells, have been reported to be successful in animal trials. However, in spite of such advances in tissue engineering, reconstruction of cranial defects are complicated by scarring, osteomyelitis, osteonecrosis, or previous radiation damage.. Also, little research explores the behavior of tissue engineering approaches in the context of extensive medical co-morbidities or compromised wound healing capability.
Research Findings